參考網址:https://blog.csdn.net/lichunericli/article/details/89060052
public static void main(String[] args) {
Map<String, Object> identity = new IdentityHashMap<>();
identity.put("A", "A");
identity.put("A", "B");
identity.put("A", "C");
Map<String, Object> identityString = new IdentityHashMap<>();
identityString.put(String.join("A", ""), "B");
identityString.put("A", "A");
identityString.put(new String("A"), "C");
MultiValueMap<String, Object> linked = new LinkedMultiValueMap<>();
linked.add("A", "A");
linked.add("A", "B");
linked.add("A", "C");
for (String key : identity.keySet()) {
System.out.println("identity:" + identity.get(key));
}
for (String key : identityString.keySet()) {
System.out.println("identity string:" + identityString.get(key));
}
for (String key : linked.keySet()) {
System.out.println("linked:" + linked.get(key));
}
}
實現原理
JDK提供的IdentityHashMap其底層是根據Key的hash碼的不同+transient Object[] table來實現的;
Spring提供的LinkedMultiValueMap其底層是使用LinkedHashMap來實現的;
LinkedHashMap的底層是使用transient Entry<K, V> head和transient Entry<K, V> tail來實現的;
Entry是LinkedHashMap的內部類,其定義方式爲:
static class Entry<K, V> extends HashMap.Node<K, V> { Entry<K, V> before; Entry<K, V> after; }
總結
IdentityHashMap和LinkedMultiValueMap的實現歸根結底就是數組和鏈表的使用。